THERMAL-EXPANSION OF BI2.2SR1.8CACU2OX SUPERCONDUCTOR SINGLE-CRYSTALS

Using a low-temperature stage X-ray diffractometer, we have investigat ed the temperature dependence of the lattice parameters of single crys tal superconductors Bi2.2Sr1.8CaCu2Ox. The experimental results show t hat (i) the lattice constants increase linearly with increasing temper ature above about 100 K; (ii) the c-axis lattice parameter shows a kin k in the superconducting transition region, while the a, b-axis parame ters do not show any anomalous behavior in this region; (iii) both a, b, and c show negative thermal expansion coefficients below 40-50 K, w hich may be related to the characteristics of the Cu-O bond.